Copper is becoming the preferred metal for interconnections, replacing aluminum and tungsten as conducting material due to its low resistivity (1.67 μΩcm for Cu, 2.65 μΩcm for Al), high electromigration resistance, and high melting point (1083° C. for Cu, 660° C. for Al). Its low interconnect resistivity may also result in faster devices.
Copper is usually electroplated inside trenches and holes in insulators; however before the electroplating step a thin continuous copper seed layer is needed. In the past sputtering techniques were used to deposit the seed layer, however due to demand for highly conformal and uniform films inside the trenches with high aspect ratios CVD- or ALD-type processes become necessary.
Several classes of Cu compounds including copper (II) bis-diketonates, copper (I) diketonate-olefin compounds, copper (I) amidinates, copper (II) aminoalkoxides, and copper (I) cyclopentadienyl complexes have been tried in CVD and ALD-type processes over the past decades. Recently, Air Liquide demonstrated excellent Cu seed layer depositions by PEALD process using copper (II) bis-ketoiminate compounds (see WO2011/006035).
The copper bis-ketoiminate compounds may be prepared either by reacting CuCl2 or CuBr2 with two equivalents of the lithium salt of the R-ketoimine ligand in tetrahydrofuran. The lithium salt reaction is shown as follows:
As shown in the comparative examples that follow, initial testing by Applicants resulted in no yield. Optimization of the method may result in some yield, but it would most likely be low.
The copper bis-ketoiminate compounds may also be prepared as described in the literature (see, e.g., P. A. Stabnikov, J. Structural Chemistry 2003, 44, 6, 1054-1061) by reacting copper acetate (Cu(OAc)2) with the R-ketoimine in aqueous alcohol in the presence of excess ammonia.
Bradley et al. disclose the synthesis of copper bis-diketiminate compounds in Example 4 of US Pat. App. Pub. No. 2008/0044687, which is summarized below.
Chen et al. disclose the synthesis of copper bis-diketiminate compounds in the hypothetical example of U.S. Pat. No. 6,620,956 by reacting CuCl2 with two molar equivalents of the lithium salt of the R-ketoimine in diethyl ether.
A need remains for improved synthesis methods for the copper bis-ketoiminate and copper bis-diketiminate compounds.